What is the function of the cornea?

The cornea is a tough, clear covering that keeps objects from entering the pupil.
The Cornea is the front part of the eye that covers the iris and the pupil.
help keep your eye clean

Keeps dirt , germs and grit out of your eye it is like the protective cover for your eye.
It refracts light together with the lens.
Because the cornea is as smooth and clear as glass but is strong and durable, it helps the eye in two ways

1. It helps to shield the rest of the eye from germs, dust, and other harmful matter. The cornea shares this protective task with the eyelids, the eyesocket, tears, and the sclera, or white part of the eye

2. The cornea acts as the eye's outermost lens. It functions like a window that controls and focuses the entry of light into the eye. The cornea contributes between 65-75 percent of the eye's total focusing power.

When light strikes the cornea, it bend-or retracts-the incoming light onto the lens. The lens further refocuses that light into the retina, a layer of light sensing cells lining the back of the eye that starts the translation of light into vision. For you to see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina. The retina converts the light rays into impulses that are sent through the optic nerve to the brain, which interprets them as images
The cornea allows light to enter the eye.
Because the cornea is as smooth and clear as glass but is strong and durable, it helps the eye in two ways 1. It helps to shield the rest of the eye from germs, dust, and other harmful matter. The cornea shares this protective task with the eyelids, the eyesocket, tears, and the sclera, or white part of the eye 2. The cornea acts as the eye's outermost lens. It functions like a window that controls and focuses the entry of light into the eye. The cornea contributes between 65-75 percent of the eye's total focusing power. When light strikes the cornea, it bend-or retracts-the incoming light onto the lens. The lens further refocuses that light into the retina, a layer of light sensing cells lining the back of the eye that starts the translation of light into vision. For you to see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina. The retina converts the light rays into impulses that are sent through the optic nerve to the brain, which interprets them as images

If I'm not mistaken, the cornea is the colorful ring surrounding the iris? I was told the cornea are the muscles that control dilation of the iris, controlling the amount of light that is allowed to enter the eye.
The reason it is colored is due to genetics. Specific amino acids produce different colors (including people like myself who's color changes, which is affected by additional acids in the food we eat).